Information for Manure and Compost Suppliers

During the past some gardeners who may have used manure containing aminopyralid residues as a fertilizer have requested additional information about the potential for herbicide residues to damage certain sensitive crops. In some instances the manure possibly came from farm animals or horses fed on pastures or hay treated with an aminopyralid herbicide.

Here is some information about aminopyralid for anyone selling manure and compost products to gardeners or landscape contractors.

What is aminopyralid?

Aminopyralid is the active ingredient in Milestone®, Milestone VM, Milestone VM Plus, ForeFront® R&P, Chaparral, GrazonNext™, Opensight and CleanWave herbicides. These herbicides are among the most effective for controlling and eliminating many rangeland and pasture weeds including thistles, ragweeds, knapweeds and star thistle.

When grassland is sprayed with aminopyralid, it kills target weeds but does not affect the grass. However, when this grass is eaten by animals, either out in the field or as hay or silage, a small amount of aminopyralid may pass through the animal in the manure and urine.

Can we accept manure from animals fed on pastures or hay treated with aminopyralid?

No. Do not accept manure from suppliers who may have used aminopyralid as this manure and the compost generated from it could have the potential to damage sensitive crops. Keep in mind that a high proportion of manure from farms and equine establishments should not contain aminopyralid residues, but check first.

Manure with suspected aminopyralid residue can be used with confidence to fertilize rangeland, permanent pastures, wheat fields and fields with grass grown for seed.

Manure with suspected aminopyralid residue must not be supplied to gardeners or farmers growing sensitive crops, such as potatoes or sugar beets.

How can we tell if there is any aminopyralid in the manure?

A bioassay test is recommended to check whether manure or compost contains residues of aminopyralid.

Does aminopyralid break down in rotting manure?

Not if the manure is stored in a heap. However, soil microorganisms will break down aminopyralid. Residues in manure will break down faster if incorporated into soil by rototilling or frequent turning of the soil.

What Can I Do?

  1. Be informed and take the necessary precautions to prevent affected manure from reaching gardens.
  2. Ask cattle and equine suppliers if they used any aminopyralid-containing herbicides on their grassland or if any of their hay or forage suppliers did.
  3. If you are selling manure that is known to contain aminopyralid, you must inform your customers, and warn them not to apply it to ground in which sensitive crops will subsequently be grown.
  4. You can supply affected manure to farmers for use on permanent pastures, wheat fields or fields where grass is grown for seed.
  5. You can test the manure.

Contact Dow AgroSciences

If you have additional questions, please contact the Dow AgroSciences Customer Information Group at 1-800-992-5994 and select Option No. 4; or e-mail